Devices for positioning or registering sheets with respect to a platen or orthogonally related surfaces are generally well known, especially in the art of making photocopying machines. See, e.g., U.S. Pat. No. 4,026,542 which discloses the use of air streams to move a sheet into registry within an abutment. Also, U.S. Pat. No. 4,469,319 discloses the use of a sheet stacking tray having a displaceable side guide abutment for accommodating sheet material of various widths in a recirculating document feeder.
In another device of this kind, U.S. Pat. No. 3,984,098 shows a device having a rectangular exposure platen and abutment strips which extend along three edges of the platen, but which are immovably connected thereto. A pressure plate is fitted between the strips for movement between a first position in which the plate is at some distance from the platen so that an original can be fed between the strips on the platen and pressed against two strips at right angles to one another, and a second position in which the plate presses the positioned original against the platen.
This device is suitable for positioning an original on the exposure platen at a fixed corner and holding it flat in that position so that the original can be copied without any loss of sharpness. However, in copying machines it is frequently necessary to position an original on the platen in one of a number of possible positions. For example, originals having different dimensions can be disposed in the copying machine with two opposite edges symmetrically with respect to the optical axis of the optical imaging system so that they can be imaged on a fixed location on the machine irrespective of the selected imaging ratio.
Accordingly, it is an object of the invention to provide a device by means of which an original can be selectively positioned on a number of locations on an exposure platen and can be pressed at those places.